Buildings, walls, industrial facilities, and transportation-related structures typically consist of shallow foundations, such as spread footings, or deep foundations, such as driven pilings or drilled shafts. Shallow foundations are much less costly to construct than deep foundations. Thus, deep foundations are generally used only if shallow foundations cannot provide adequate bearing capacity to support building weight with tolerable settlements.
Recently, ground improvement techniques such as jet grouting, soil mixing, stone columns, and aggregate columns have been used to improve soil sufficiently to allow for the use of shallow foundations. Cement-based systems such as grouting or mixing methods can carry heavy loads but remain relatively costly. Stone columns and aggregate columns are generally more cost effective but can be limited by the load bearing capacity of the columns in soft clay soil.
Additionally, it is known in the art to use metal shells for the driving and forming of concrete piles. One set of examples includes U.S. Pat. Nos. 3,316,722 and 3,327,483 to Gibbons, which disclose the driving of a tapered, tubular metal shell into the ground and subsequent filling of the shell with concrete in order to form a pile. Another example is U.S. Pat. No. 3,027,724 to Smith which discloses the installation of shells in the earth for subsequent filling with concrete for the forming of a concrete pile. A disadvantage of these prior art shells is that their sole purpose is for providing a temporary form for the insertion of cementitious material for the forming of a hardened pile for structural load support. The prior art shells are not extensible and thus do not exhibit properties that allow them to engage the surrounding soil through lateral deformations. Further, because they relate to the use of ferrous materials, which are subject to corrosion, their function is complete once the concrete infill hardens. Thus, the prior art shells are not suitable for containing less expensive granular infill materials such as sand or aggregate, because the prior art shells cannot laterally contain the inserted materials during the life of the pier. The prior art shells are also not permeable and are thus ill-suited to drain cohesive soils.
Accordingly, it is desirable to provide improved techniques for constructing a shallow support pier in soil or the ground using extensible shells formed of relatively permanent material of a substantially non-corrosive or non-degradable nature for the containment of compacted aggregate therein.